1. Technical Field
The present invention relates to an impact absorbing structure that absorbs impacts acting upon a vehicle.
2. Related Art
In recent years, automobiles have proliferated in which a bumper beam is supported by a energy absorbing member (crush box) on a vehicle body in order to absorb impacts during collisions or the like. In addition to energy absorbing members made from steel, for example, some members are made from fiber-reinforced plastics (FRP) and carbon fiber-reinforced plastics (CFRP), as described in Japanese Unexamined Patient Application Publications No. H6-300068 and H8-170675.
The abovementioned energy absorbing members are formed in a cylindrical shape and a plurality of layers is laminated in the radial direction thereof. When a strong impact acts that can fracture the vehicle body, interlayer fracture (peeling) successively occurs in the energy absorbing member from one end to the other end in the axial direction, thereby absorbing the impact energy (progressive crushing).
However, if a load acts unevenly on the energy absorbing member, for example, such that the load acts obliquely with respect to the axial direction, the expected energy absorption characteristic cannot be demonstrated. Accordingly, comprehensive research and development have been conducted to demonstrate the energy absorption characteristic at its maximum.
The design of the joint of the energy absorbing member and the bumper beam differs depending on the barrier shape during a collision test. In particular, in the case where an offset collision is taken into account, a joint that joins the bumper beam and the energy absorbing member is provided and the tip of the joint has an inclined shape that is inclined from the center of the vehicle outward in the width direction. As a result, even when a collision load acts obliquely with respect to the bumper beam, the joint and the energy absorbing member can be reliably collapsed in the longitudinal direction and the load can be caused to act uniformly on the energy absorbing member.
However, in the case the tip of the joint is thus provided with an inclined shape with consideration for an offset collision, a crushing remainder may appear at the tip of the inclined shape in the joint at the time of a full-wrap collision. If the crushing remainder appears in the joint, the collapse propagation is blocked and a collision load equal to or greater than a set load locally acts upon the energy absorbing member before the joint collapses, whereby the amount of absorbed energy is decreased.
As describe above, in order to ensure a large amount of absorbed energy with respect to collisions of various modes, such as a full-wrap collision, while demonstrating the energy absorption characteristic at its maximum at the time of an offset collision, it is necessary too investigate the material, strength, and shape of the joint for each condition, whereby designing work becomes extremely complicated.